1. Field of the Invention
The present invention relates to a magneto-resistive (MR) element and its production method, an MR head and magnetic recording/reproducing apparatus and in particular, a magneto-resistive (MR) element for reading an information signal recorded on a magnetic recording medium and its production method, an MR head and a magnetic recording/reproducing apparatus.
2. Description of the Related Art
Conventionally, there has been disclosed a magnetic reading converter called an MR sensor or MR head as a technique of a hard disc drive. These can read a data from a magnetic surface with a large linear density.
The MR sensor detects a magnetic field signal according to a resistance change as a function of intensity and direction of a magnetic flux detected by a read element. Such a conventional MR sensor operates according to the effect of anisotropic magneto resistance (AMR) in such a way that a component of resistance of the read element changes in proportion to square of cosine of the angle between the magnetization direction and the sense current direction flowing in the element. The AMR effect is detailed in D. A. Thompson xe2x80x9cMemory, Storage, and Related Applicationsxe2x80x9d, IEEE Trans. on Mag. MAG-11, p 1039 (1975).
In a magnetic head using the AMR effect, longitudinal bias is often applied in order to suppress the Barkhausen noise. The longitudinal bias may be realized by an antiferromagnetic material such as FeMn, NiMn, nickel oxide or the like.
Furthermore, more remarkable magnetoresistivity has been disclosed. That is, the resistance change of a layered magnetic sensor is based on a spin dependent transmission of conductive electrons between magnetic layers via a non-magnetic layer and accompanying spin dependent scattering on the layer boundary. Such a magnetoresistivity is called xe2x80x9cgiant magnetoresistivityxe2x80x9d, xe2x80x9cspin bulb effectxe2x80x9d, and the like. Such an MR sensor is made from an appropriate material and enables to improve sensitivity and increase the resistance change in comparison with a sensor using the AMR effect.
In this type of MR sensor, the resistance of a plane between a pair of ferromagnetic layers separated by a non-magnetic layer changes in proportion to the cosine of an angle defined by the magnetization directions in the two ferromagnetic layers.
On the other hand, Japanese Patent Publication 2-61572 discloses a layered magnetic configuration which brings about a high MR change generated by anti-parallel arrangement of magnetization in the magnetic layers. The layered configuration is made from ferromagnetic transition metals or alloys. Moreover, it is disclosed that at least one of the two ferromagnetic layers separated by an intermediate layer preferably has a fixing layer added and that the fixing layer of the magnetization direction is preferably formed from FeMn.
Japanese Patent Publication 4-358310 discloses that in an MR film having a basic configuration of a ferromagnetic layer, a non-magnetic layer, and a ferromagnetic layer, the areas of the two ferromagnetic layers (free layer and fixed layer) are identical to the area of the non-magnetic layer and a detection current is made to flow in parallel to the film surface.
The IEEE Transactions on Magnetics, vol. 33, No. 5, September 1997, pp 3505-3510, for example, discloses in an MR film having a basic configuration of a ferromagnetic layer, a non-magnetic layer, and a ferromagnetic layer, the areas of the two ferromagnetic layers (free layer and fixed layer) are identical to the area of the non-magnetic layer and a detection current is made to flow vertically to the film surface.
FIG. 18 shows a representative conventional magneto-resistive (MR) element. As shown in FIG. 18 (a), a non-magnetic layer 103 is sandwiched by a first magnetic layer 101 and a second magnetic layer 102. Moreover, as shown in FIG. 18(b), the first magnetic layer 101, the second magnetic layer 102, and the non-magnetic layer 103 have end surfaces as ABS (air bearing surface).
FIG. 19 shows an example of the magneto-resistive (MR) element of FIG. 18 applied to a reproduction head. As shown in FIG. 19(a), the magneto-resistive (MR) element includes a fixing layer 105, a fixed layer 101a, a non-magnetic layer 103, and a free layer 102a which are sandwiched by a longitudinal bias layer 106. On the longitudinal bias layer 106, electrodes 108a and 108b are provided. Moreover, as shown in FIG. 19(b), the fixed layer 101a, the free layer 102a, and the non-magnetic layer 103 have end surfaces as ABS.
However, such a conventional magneto-resistive (MR) element having a basic configuration of the free layer, the non-magnetic layer, and the fixed layer has various problems. As is clear from FIG. 19(a) and (b), when viewed from the top, in the conventional configuration, the free layer 102a has an identical area to the fixed layer 101a. 
In such a magneto-resistive (MR) element, when a sense current is made to flow in a horizontal direction (CPI: current in the plane), before electrons are sufficiently spin-polarized in one of the free layer 102a and the fixed layer 101a, the electrons move to the other layer. Thus, only much smaller resistance change is obtained than can be expected from the magnetic materials used.
On the other hand, in a magneto-resistive (MR) element in which sense current is made to flow vertically (CPP: current perpendicular to the plane), when the free layer 102a and the fixed layer 101a have a sufficient thickness, the electron spin-polarization is sufficiently realized and it is possible to obtain a resistance change near to the one that can be expected originally.
However, when an actual application as a reproduction head is considered, the free layer 102a preferably has a small thickness for critical sensitivity increase. Moreover, the fixed layer 101a also preferably has a small thickness, because this increases the value of exchange coupling field applied from the fixed layer 101a to the fixing layer 105 adjacent to the fixed layer 101a and opposite to the non-magnetic layer 103, and improves the magnetic stability of the fixed layer 101a. Furthermore, when the free layer 102a and the fixed layer 101a have a small thickness, the static magnetic coupling between these layers is reduced, which facilitates zero point positioning at magnetic field zero applied.
Consequently, in the CPP, the free layer 102a and the fixed layer 101a should have a film thickness as thin as possible. However, if the film thickness is small, there arises a problem that the resistance change is significantly decreased.
As has been described above, the conventional configuration including CIP and CPP provides a resistance change much smaller than can be expected from the material band configuration of the free layer 102a and the fixed layer 101a. 
It is therefore an object of the present invention to provide a magneto-resistive (MR) element which enables to obtain a higher reproduction output than in the conventional magneto-resistive (MR) element and which can be produced with a higher yield, and a production method thereof, an MR head and a magnetic recording/reproducing apparatus.
The magneto-resistive (MR) element according to the present invention comprises: a first magnetic layer provided on a substrate; a non-magnetic layer arranged to be in contact with the first magnetic layer; and a second magnetic layer arranged to be in contact with the non-magnetic layer; wherein sense current flowing in the first and the second magnetic layer is changed by a resistance change according to an external magnetic field, and a sense current flowing distance in the first magnetic layer and/or a sense current flowing distance in the second magnetic layer is longer than a sense current flowing distance in a superimposed portion of the first magnetic layer, the non-magnetic layer, and the second magnetic layer.
When the substrate is viewed from a direction vertically intersecting the main surface of the substrate, the superimposed portion of the first magnetic layer and the second magnetic layer may have an area smaller than each of the first magnetic layer and the second magnetic layer.
On the other hand, the MR head according to the present invention comprises: a magneto-resistive (MR) element claimed in claim 1 or claim 2 and provided on a substrate; a first electrode mounted on the first magnetic layer; a second electrode mounted on the second magnetic layer; and a fixing layer arranged to be in contact with the first magnetic layer for fixing the magnetization direction of the first magnetic layer.
On the other hand, the magnetic recording/reproducing apparatus according to the present invention comprises: a magnetic recording medium having a plurality of tracks for recording a data; a magnetic recording head for storing data in the magnetic recording medium; the MR head claimed in claim 3 or 4; and actuator means for moving the magnetic recording head and the MR head to a desired track on the magnetic recording medium.
Moreover, the magnetic recording medium may be a hard disc.